The invention relates to a hydraulically actuated disc brake having at least two brake pistons acting upon a brake lining (pad), which pistons are arranged in a brake housing.
Even in the case of disc brakes with two or more brake pistons, oblique wear or circumferential oblique wear of brake linings (pads) can occur, which constitutes a factor limiting the service life of the brake linings. Pneumatically actuated disc brakes with two brake pistons are equipped with a mechanical synchronization of an adjusting movement of the two brake pistons, which are also referred to as actuating rams or adjusting spindles. Such a measure can serve to increase the service life of the brake linings by up to 25%.
Further measures are known for preventing oblique wear in pneumatically applied disc brakes, such as an offset tightening force introduction, for example; a pulled-on brake lining, which carries the disadvantage, however, that the brake caliper has to be dismantled when changing a brake lining, which should not be used for commercial vehicles; and a so-called suspended pressure plate.
All of these approaches to a solution, however, relate to pneumatically actuated disc brakes. No oblique wear reduction by means of synchronized adjustment of the actuating or brake pistons is known to exist for hydraulically actuated multi-piston disc brakes. The oblique wear occurring is a factor in the service life, particularly in the case of commercial vehicle disc brakes with hydraulic actuation.
DE 10 2005 049 786 A1 describes a self-energizing disc brake, in which a stepped piston applies pressure to two actuating pistons in order to vary wedge angles. The dimensions of the step cross sections of the stepped piston are designed so that in conjunction with operating mechanisms they give rise to different displacements of the actuating pistons when the stepped piston is shifted.
The object of the present invention therefore is to improve a hydraulically actuated multi-piston brake so as to minimize the effect of the oblique wear.
The object is achieved by a hydraulically actuated disc brake with at least two brake pistons acting upon a brake lining. The two pistons are arranged in a brake housing. A hydraulic synchronization device for reducing oblique wear of the brake lining is interposed between an input pressure line for brake actuation and the brake pistons.
A hydraulically actuated disc brake according to the invention, having at least two brake pistons acting upon a brake lining, which are arranged in a brake housing, is characterized in that the hydraulically actuated disc brake includes a hydraulic synchronization device for reducing oblique wear of the brake lining. The hydraulic synchronization device is interposed between an input pressure line for brake actuation and the brake piston. Accordingly, no mechanical moving components are needed, such as adjusting screws and associated mechanisms, for example. The hydraulic synchronization device is therefore provided with only a small number of components, for example a stepped piston, which is fitted in the brake housing between the brake pistons.
The hydraulic synchronization device may be fitted at least partially in the brake housing, thereby saving space.
In a preferred embodiment the hydraulic synchronization device is designed with a stepped piston, which includes the following:
(1) at least a first piston face, which can be subjected to an inlet pressure for brake actuation and which is moveably arranged in an inlet pressure chamber; and
(2) at least two piston faces for generating an actuating pressure for each of at least two brake pistons, which are each moveably arranged in a corresponding outlet pressure chamber.
The stepped piston is here arranged between the two brake pistons in the brake housing, so that in order to obtain short line distances, that is to say in order to reduce the flow resistances, the outlet pressure chambers of the synchronization connected to the actuating cylinders or pressure chambers of the brake pistons are made to face towards the former. The inlet pressure delivered by the brake master cylinder of the brake system in a brake actuation acts on the first piston face of the stepped piston, which thereupon with its second and third piston faces generates pressures for the respective brake pistons.
In the case of an unevenly worn brake lining, the force begins to build up earlier on the brake piston belonging to the thicker side of the brake lining than on the brake piston belonging to the thinner side of the brake lining, and the rise in pressure in the associated pressure chamber thereby also occurs earlier than on the other chamber, which is associated with the thinner side of the brake lining. In the further course of actuation, different pressures form in the two pressure chambers due to the synchronous actuation of the stepped piston, with the result that actuating force of the piston on the thinner side of the brake lining diminishes and that of the piston on the thicker side is increased. In this way, the wear inside the brake lining is evened out. This unequal distribution of the piston force increases until no further increase in the unequal wear occurs.
In one embodiment, the outlet pressure chambers are advantageously connected to the inlet pressure chamber, in order to afford a wear adjustment or clearance adjustment after brake servicing, a brake servicing piston reset facility, a facility for filling the brake system during initial assembly and brake servicing, and a so-called soft ‘knock-back’ for preventing DTV, all of which are necessary functions.
In a further embodiment, in a resting position of the stepped piston, the output pressure chambers are interconnected and at least one outlet pressure chamber is connected to the inlet pressure chamber.
The outlet pressure chambers are more preferably still connected to the inlet pressure chamber by way of controllable connections, the controllable connections having at least one valve. This valve may be a pressure-controlled valve, for example one controlled by the inlet pressure.
The valve is more preferably still a remotely controlled valve. This may be actuated by a solenoid, for example. This is a simple way of achieving a continuous synchronization, a suitable wear adjustment, a facility for resetting the piston when servicing the brake, a facility for filling the brake system with hydraulic fluid and a soft ‘knock-back’.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.